Messenger-no6

THE MESSENGER

No. 6 - September 1976

Mechanical Assembly of 3.6 m Telescope Completed The 3.6 m telescope erection is proceeding weil, informs Dr. Laustsen from La Silla. His report was written on the first day of August: By the end of July, the mechanical erection of the telescope was nearly completed. Three weeks earlier, the team of Creusot-Loire had installed the upper ring onto the Serrurier struts of the tube. The "machine" thereby recuperated its proper appearance-it looks again like areal telescope. Three months of hard work were spent to reach that stage. More than 150 crates were opened and piece after piece of the telescope was transported the last 1.5 km from the un-

packing area up to and then into the telescope building. Cleaning and assembly work was normally done on the ground floor before the 35-ton crane of the dome took over

Aerial view of the 3.6 m dome on the summit of La Silla, July 1976.

PhOIO by S. Laustsan and R. Oonarsky.

and lifted the piece up through the shaft to the observing floor. A few pieces, or sub-assemblies, weighed more than 30 tons. The heaviest one, the assembled horseshoe, weighed about 40 tons and was, with great care, used as a test load, before the crane was entrusted with the task to lift the piece into place. Thanks to the fact that a pre-assembly was made in Europe, the assembly work on La Silla went through pretty smoothly. Problems were mainly encountered in areas where tests could not be completed in Europe, and then, as one could expect, in the inferface between building and telescope. Some of the problems gave rise to a few days' extra work. Nothing more important was encountered so far. During the last days of July, the telescope was turned around both polar axis and declination axis by means of a simple motor control box. The control system for the telescope has been installed in the building, and the cabling, which is a huge job, is weil advanced. August is going to be a busy month for the Electronics Group; and in September we expect to install the main mirror and start with the Hartmann tests. The aluminizing plant ist being installed these days. But about these activities we shall report later.

PROFILE OF A VISITOR'S PROGRAMME:

OH/IR Sources Astronomers trom the Max Planck Institute tor Radioastronomy (MPI) in Bonn, Fed. Rep. ot Germany, have recently succeeded in measuring intrared (IR) radiation trom OH radio sources (emission trom the hydroxyl radical). Dr. W. A. Sherwood reports about the signiticant progress made in this exciting programme: In July 1968 Wilson and Barret! at MIT discovered OH radio emission from some infrared (IR) stars. The rate of detection for prime candidates was about 10 %, but later the rate fell to 5 % in a larger sam pie. My colleagues at MPI have also searched for OH in IR stars selected to have very late spectral types, extreme red colours and large amplitude variations in the infrared from 1 II to 20 ~l and have had a very high success rate in a small sampie. The reason for the sm all sam pie ist that the criteria are almost mutually exclusive: for the spectral type to be known, the object must be visible, implying less than extreme reddening. In addition very few objects have been sufficiently observed for the criteria to be met. There are predominantly two types of OH radio emission associated with IR stars: one of the main lines (1665 or 1667 MHz) or the satellite line at 1612 MHz is the strongest. The OH emission associated with the latter type shows the following characterislics: 1. The line profile is usually split into two components separated by 10 to 50 km/s- 1 •

4. Une components are narrow having widths between 1 and 6 km/s- 1 . 5. Most sources vary (OH and IR apparently in phase). Early in the 1970s OH mappi ng su rveys at 1612 MHz were started. What we now wondered was whether all OH sources having these criteria also had IR stars. Up to the 1973 lAU General Assembly in Sydney, searches for the IR stars had largely been unsuccessful for two reasons: the uncertainty in the radio coordinates for the new OH sources was too large and the wavelength of 2.2 ~l used for the IR search was too short. The high brightness temperature in contrast to the low temperature derived from the line width implied maser excitation. The lack of a radio continuum source suggested to us that the infrared pumping mechanism rather than another mechanism, such as collisional excitation, was a possibility. The pump could operate at 2.8 ~l, 35 ~l or at longer wavelengths. Since the IR stars in which OH emission had been discovered were bright at 2.2 ~l, the 2.8 ~l mechanism was considered to be the likely one and searches were made at the 2.2 ~l atmospheric window. On the other hand, Georg Schultz noticed that the IR sources with OH had a larger infra red excess at 3.511 than at 2.2 ~l, and because, too, our equipment initially wasn't very sensitive. he made a successful pilot survey without filter to detect sources wh ich are brig hter at wavelengths longer than 2.2 ~l. In order to make firm identifications of the OH sources with IR stars. it was necessary to improve the accuracy of the radio coordinates to ± 10-15 arcseconds using the 100 m telescope at Effelsberg. It was also necessary to improve the method of determining the optical coordinates on the ESO 1 m telescope on La Silla-in the infrared one requires an astrometric photometric telescope, since the objects can only be found by scanning or setting on accurately-known positions. The effort pays off in increased efficiency, meaning more observing time. Our day-time success is a result of this effort and was reported by Willem Wamsteker of ESO in the June 1976 issue of the Messenger. Using the ESO 1 m telescope and infrared equipment developed by Ernst Kreysa, we scanned at 3.8 ~l 30 sources from the list of Anders Winnberg. Before our run in J uly 1976 we had discovered 50 % of the expected number of IR sources. The Table shows that the detection rate is clearly a function of the brightness of the OH sources. In July with more sensitive equipment we detected a few more sources but the 100 % level may require the use of the ESO 3.6 m telescope.

FREQUENCY OF DETECTING OH SOURCES SEARCHED AT 3.8 ~l NO.ol OH sources scanned

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M ulticoulor photometry for a few objects suggests that our sam pie of OH/IR objects are redder than the previously known ones. Some of the sources are up to 100 times fainter at 2.211 than they are at 3.711. In at least two objects the intensity appears to be still rising even at 2011. Winnberg's OH survey yielded the most sources within 1/2 of the galactic plane. The IR magnitudes and colours plus the local standard-of-rest velocities indicate that the new objects are reddened distant objects, perhaps more luminous on the average than the objects first found by Wilson and Barrett. At this stage we may divide our research into two parts: the specific and the general study of OH/IR sources. In the specific study we note that the OH survey ist statistically complete between 18" ~ I ~ 50 with Ibl = 10 and in order to analyse the data the IR observations ought to be as complete as possible: 100 % of all the IR sources, extended wavelength coverage (1 11 to 3511 from the earth) and increased resolution in both wavelength and time. We have OH and IR

observations at 6-month intervals extending over 18 months and know that the sources vary. The variation (phase and amplitude) contains information about the pumping mechanism, mass loss and the density of the dust cloud surrounding the star. We hope to derive the absolute luminosity, distance and reddening of each system. In the general study the OH/IR sources are probes in the study of the dynamics of the Milky Way. We are working with Dutch and German astronomers in identifying the IR counterparts of those high-velocity OH/IR sources found ne ar the galactic centre. This project is complimentary to the one described by Blaauw in the June 1976 issue of the Messenger. Combining IR distances with OH radial velocities will allow a detailed study of the gravitational potential and mass distribution of the central part of the Galaxy while the McCormick Areas Programme is a study of the "Iocal" galactic evolution.

Swiss Astronomers on La Silla Last year saw the installation of a Swiss telescope on La Silla and the arrival of the first observers. Here Dr. F. Rufener, of the Geneva Observatory, teils about the telescope and some of the observing programmes which are being carried out:

The Geneva Observatory station on La Silla.

Following aconvention established in 1974, theCouncil of ESO has authorized the Geneva Observatory to set up a provisional observing station on La Silla. It has an Ash-dome of 4.60 m diameter which is linked to a working-site hut. This hut was shipped to La Silla as a container and consists of a sheltered observation post, a workbench with emergency repairs equipment and a kitchenette. The dome protects the equatorial table on wh ich a Cassegrain telescope of 40 cm apert ure and 7.20 m focal length has been mounted. The controls of the equatorial table allows an accurate setting by the reading of the digital display of the celestial coordinates (right ascension and declination). A special control panel situated near the strip-chart recorder offers the observer offsetting facilities (small-angle displacement of the telescope).

The Telescope

The 40 em Cassegrain teleseope 01 the Geneva Observatory on La Silla. The photoeleetrie photometer is at the Cassegrain loeus.

The telescope is equipped with a classical photoelectric photometer on which UBV B, B2 V, G filters of the photometric system of the Geneva Observatory have been mounted. The acquisition procedure is very simple; measures in direct

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current are made through an amplifier with total counterreaction and an analogue recording on roll-paper. A calibration device allows to check the dynamics of the sensitivity ranges (104 ). Presently. this instrument obtains accurate photometric observations, in seven colours, for stars of magnitude 4 ~ mv ~ 10. An achromatic attenuator

Visiting Astronomers

Several astronomical programmes are undertaken and pursued simultaneously. Of great importance is the establishment of a network of standard stars in the southern sky, which must be rigidly tied-in magnitude and in colours-to our standard stars in the northern sky. We also want to complete a variety of stellar sam pies al ready observed in the northern hemisphere, e.g. stars in the solar neighbourhood, the brighter stars, O-stars, B-stars of known distances (i.e. in the Scorpius-Centaurus association) and the stars of peculiar chemical composition. Some fields close to the southern galactic pole are observed methodically. We are also interested, in connection with stellar structure studies currently undertaken in Geneva, in having many, very complete and very accurate sequences of open star clusters. Since the 10th November 1975, when this installation entered into operation, teams of two observers of the Geneva Observatory take turns on La Silla. They carry out the observations and the maintenance of the equipment. Several thousands of the measurements in seven colours have al ready been obtained and reduced in Geneva. The photometric quality of the site is really remarkable, and the number of clear nights is so high that it can be very tiring even for our best teams!

Jan. 1977:

Denoyelle, Haug, Wamsteker, Borgman, Wh~rick, Adam, Breysacher/Muller/Schuster/West, Tinbergen.

Feb.1977:

Tinbergen, Vogt, Kohoutek, Danks, Chevalier

(Oetober 1976-Mareh 1977) Observing time has now been allocated lor period 18 (October 1. 1976 to April 1, 1977). The demand lor telescope time was again much greater than the time actually available. This abbreviated list gives the names 01 the visiting astronomers, by telescope and in chronological order. The complete list, with dates. equipment and programme titles, is available at request lrom ESO/Munich.

152 em Speetrographie Teleseope Oct. 1976:

Breysacher/Muller/Schuster/West. v. d. Heuvel, Maurice,

Nov.1976:

Maurice, Seitler, Divan. Chincarini/Materne. Breysacher/Muller/Schuster/West. Pakull.

Wamsteker,

Dec. 1976:

Pakull, Westerlund/Olander, Ardeberg/Lyngä/Cullum, Bergwall/Ekman/Lauberts/Westerlund, Denneleld. Materne.

Jan. 1977:

Materne, Denoyelle. Havlen/Quintana. Breysacher/ Muller/Schuster/West, Breysacher/Westerlund. J. P. Swings.

Feb.1977:

J. P. Swings, Kohoutek, AIIoin, MoffatlSolf/Kohoutek.

March 1977: MollatlSolf/Kohoutek, Gieren, Havlen.

1I0vaisky,

Wamsteker,

100 em Photometrie Teleseope Oct. 1976:

Havlen, Breysacher/Muller/Schuster/West, Mianes/Rousseau/Rebeirot.

Nov. 1976:

Mianes/Rousseau/Rebeirot, Wamsteker, Crane. Chincarini/Materne, Alcaino. Crane, Westerlund/ Olander.

Dec. 1976:

4

Westerlund/Olander, Pakull, Ardeberg, Maitzen, Alcaino.

March 1977: Chevalier. Wamsteker, Wamsteker, Vogt.

Chevalier,

Sherwood.

50 em ESO Photometrie Teleseope Oct. 1976:

Duerbeck.

Nov.1976:

Duerbeck, Seitler. Pakull, Eist.

Dec. 1976:

Eist, Heck, Vogt. Heck, Vogt.

Jan. 1977:

Heck. Haug, Borgman, Vogt.

Feb. 1977:

Knoechel. Vogt, Manlroid, Vogt, Krautler.

March 1977: Krautler, Gieren. 1I0vaisky.

Objeetive Prism Astrograph (GPO) Oct. 1976:

Blaauw/West, Azzopardi, Heudier, Muller/Schuster/West.

Nov. 1976:

Pakull. Blaauw/West, Heudier, Muller/Schuster/ West.

Dec. 1976:

Zeuge. Blaauw/West, Zeuge, Gieseking, Heudier.

Feb.1977:

Blaauw/West, Gieseking, Muller/Schuster/West.

March 1977: Amieux, Denoyelle, Gieseking, Muller/Schuster/West.

Blaauw/West,

60 em Boehum Teleseope Dec. 1976:

Hardorp, Oblak.

50 em Danish Teleseope Jan. 1977:

Haug, Kohoutek.

Feb.1977:

Kohoutek, Sterken/Jerzykiewicz, Renson.

March 1977: Renson.

The ESO Optics Group and some Recent Achievements R. N. Wilson

DEVELOPMENT OF THE OPTICS GROUP The ESO Optics Group was formed in March 1973. The need was already pressing at that time with many problems connected with the optical tolerancing and testing of the 3.6 m telescope requiring urgent attention. Also required was a major optical design effort on prime focus correctors and ancillary optics for the adapters (interface units between astronom er and telescope providing viewing, guiding, focusing and other facilities). The auxiliary instrumentation programme, then in its initial phases, also placed heavy demands-not only for optical design, but also on basic layout determined by the astronomical/optical interface.

It became evident very early that the founder member of the OG, Ray Wilson, could not cope alone with this large and increasing volume of work.The first extension of the OG was Francis Franza, a technical assistant in mechanics, who joined us in January 1973. His first major task was the opto-mechanical layout of the prime focus and Cassegrain adapters in collaboration with the (then) coordinator, Bernth Malm. At the end of 1973 an extremely powerful optical design programme, ACCOS V, was purchased from the USA. This was put into use with the CERN CDC 7600 computer and rapidly proved a most powerful and efficient tool. However, a full-time optical designer was required to exploit it. In September 1974, Maurice Le Luyer, one of France's most ex perienced optical designers, joined the OG. He took over responsibility for the whole optical design and computer side of the OG operations. The most urgent tasks were the computation of the adapter optics and the prime focus correctors. The decision had been taken in late 1972 to build an optics laboratory next door to the mechanics assembly hall. It was the group leader's philosophy from the start that optical manufaeture was not a sensible field of activity for ESO, since there is ample manufacturing capacity available in industry. The role of the laboratory was thus to be principally optical assembly and testing. To take charge of the Optics Laboratory, equip it and assume responsibilities in the mounting load of work in auxiliary instrumentation, Daniel Enard was engaged in February 1975. At the same time Guy Ratier joined the OG for a year, on leave from the Pic-du-Midi Observatory. Guy's main task was to advance the design of a coude spectrometer as weil as assisting with the adapters and with certain specialized problems connected with the 3.6 m telescope. Until this year, it had been impossible for the OG to take any significant interest in existing equipment in Chile-the manpower simply did not permit it. However, contact was established by a visit by Ratier in 1975 and by Enard and Wilson in February 1976. The major purpose of the latter visit was to prepare the way for the installation and test phase of the optics of the 3.6 m telescope. A fruit of this contact has been the decision to engage an optical engineer for La Silla. Max Lizot will be joining the Operations Group in August 1976. He will not be a formal member of our OG but will maintain very close liaison with us to the mutual benefit, we are confident, of both ESO-Geneva and ESO-La Silla. To

complete the basic manpower of the OG, an optical technician will be engaged within the next few weeks. His work will be the assembly and test of equipment in the Optics Laboratory.

SOME RECENT ACHIEVEMENTS 1. Telescope Optics The end of the current year should mark the end of an era for the OG in which the requirements of the 3.6 m telescope have dominated our activities. Several man-years of capacity have been devoted to the adapters alone in one way or another. The simplified prime toeus adapter, designed round the Gascoigne plate corrector, has recently been assembled and adjusted and has now left for Chile. It is an essential element in the initial prime focus use of the telescope. A major effort of assembly, adjustment and test will take place over the next few months on the Cassegrain adapter, for which the optics was recently delivered. A prime focus adapter tor the triplet eorreetor is under development. After considerable design analysis, it was decided to equip the telescope with two types of prime focus corrector. (It should be remembered that the naked primary of our quasi-Ritchey-Chretien telescope does not yield a corrected image without corrector.) The first type is called the Gaseoigne plate (GP) and provides a field of about 00 25 with a single aspheric plate. Two such plates have been manufactured, one optimized for the red spectral region and one for the blue. These ESO plates are among the first to be made: the manufacture is difficult and its success depends on a rigorous test procedure. A special optical system for this test was developed in the OG. The GPsshould provide maximum efficiency correctors with particularly good ghost-image performance. Combined with an electronographic image tube (Spectracon), they should give maxim um penetration into space for photographic work. The triplet correctors (again a "red" and "blue" one) are currently being manufactured and will be available for integration into the adapter towards the end of this year. They will provide a field of 10 with rather stronger ghost images and will be used with classic photographic plates (or perhaps film) where a larger field is useful. Ooublet correctors, giving intermediate characteristics, have also been calculated, but it is feit that the others cover sufficiently our present requirements.

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Fig. 1. Hartmann plate for 1/5 paraboloid of 600 mm diameter tested at centre 01 curvature.

2. Testing and Adjustment 01 Telescopes and Other Optics Telescopes are very expensive instruments. The quality demands placed on the manufacturer of the optics are considerably more severe than those customary before the last war. Such quality is only possible or verifiable with highly sophisticated test procedures. The standards of test and adjustment in maintenance must be correspondingly high, otherwise the heavy economic investment in potential quality is wasted in astronomical practice. The expected performance of the 3.6 m telescope on the basis of existing test material has been analysed in great detail. In particular, the prime mirror support system has been the subject of a careful analysis which suggests that the telescope should, even with the least favourable interpretation, be weil within the specification. The final quality will be known before the end of this year. A comprehensive adjustment and test schedule has been planned, based on visual and photographic tests but above all on Hartmann testing with a 2-dimensional screen. This rigorous test procedure, pioneered in its general 2-dimensional form at Lick, Kitt Peak and the Optical Sciences Center in Tucson, provides a means of analysing telescope quality in scope and precision quite impossible in the pre-computer era. A basic programme kindly supplied by Kitt Peak has been considerably extended to give comprehensive analysis of the different possible errors which can affect the image due to manufacturing irregularities in the mirror surfaces or distortions of cells or the tube. This development is certainly one of the most important undertaken by the OG. Apart from the computer side, it requires sophisticated plate-measuring equipment with computerized output. Such facilities exist in the Sky-Atlas Laboratory in Geneva and similar developments have been undertaken by ESO-Chile for plate

6

measurements at La Silla. Trial Hartmann tests have been performed on the 1 m telescope of the Pic-du-Midi and on the ESO 1 m photometric telescope. Routine Hartmann testing should have a major impact in future in maintaining high optical quality of all ESO telescopes. An analogous programme development which is also of great significance allows the computer analysis of interferograms. Such interferograms provide one of the best methods of establishing the quality of optical elements and systems. Such analysis has already been of great value in assessing the quality of the Gascoigne plate correctors and of parabolic mirrors destined for use in holographic grating production. It is not possible in a general article like this to go into details of Hartmann or interferometric testing. However, it is instructive to see what a typical Hartmann plate and interferogram look like and what computer analysis produces. Figure 1 shows a Hartmann plate exposed for an f/5 parabolic mirror, tested in auto-collimation at its centre of curvature. A screen containing a set of holes in a rectangular mesh arrangement is placed in front of the mirror and a photographic plate placed near, but not at, the pinhole image at the centre of curvature. If the mirror were a perfect sphere, the image would be perfect and the Hartmann plate produced would be a perfect reproduction on a sm all scale of the screen. Aberration of the image produces distortions of the positions of the spots. In this case, the major barrel-type distortion does not correspond to errors of the mirror, but to aberration produced by its desired parabolic form. If the spot coordinates are measured with an accurate measuring machine, a sophisticated computer programme can analyse the errors in terms of a defined polynomial with a statistical or higher order residual. After removing the term corresponding to lhe parabolic form,

Fig. 2. Interlerogram 01 same 1/5 paraboloid tested at centre 01 curvature with compensating lens to remove spherical aberration.

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a perfect wavefront in wavelengths as units.

the analysis reveals in this case that the most serious error is astigmatism of about 0.75 i. ( i. = wavelength of light 500 nm). The interferogram (Fig. 2) is of the same mirror, but with the important difference that the aberration caused by the parabolic form has been removed by a compensating lens. The errar in straightness of the fringes thus represents the manufacturing errars directly. The astigmatism is only obvious to the practised eye, but the central "hole" in the wavefront is very evident. Figure 3 shows a contour map of the wavefront compared with a perfect sphere. This is part of the output from the Computer analysis. In this case, the map was deduced fram

the interferogram, but an analogous map can be obtained from the Hartmann plate. This map shows clearly the basic "saddle" form corresponding to astigmatism.

3. Optics Laboratory Telescope testing is perhaps the most important application, but many such Hartmann plates and interferograms will be produced, as with the paraboloid discussed above, in our own Optics Laboratory shown in Figure 4. Apart from normal small equipment of optical benches, light sources, etc., the main equipment consists of a Matra "Acofam" Optical

7

Test Sench, which permits detailed analysis of lens systems, a heavy optical bench in stone, a Laser Unequal Path Interferometer and a photometer. The photo also shows a HP 2100 computer of the sort which will be used for the controls of the 3.6 m telescope and for Hartmann analysis.

4. Auxiliary Instrumentation tor the 3.6 m Telescope A word should now be said about recent work on auxiliary instrumentation, without which the utility of the telescope would be very limited. We make no attempt here to list or discuss the instrumentation programme in general (such an article will appear in a future issue), but mention only those projects on which the OG has worked. A conceptual design has been worked out for a coude echelJe spectrometer, and this has been approved by the Review Team advising on the project. The detailed design study will be pursued as soon as the 3.6 m initiation phase is complete. Similarly, a conceptual design for a Cassegrain echelJe spectrograph has been prepared for discussion in the appropriate Review Team. Optical design work is under way on a tocal reducer for the prime focus of the 3.6 m telescope.The optics of the coude auxiliary telescope (CAT) will be tendered within the next few weeks. A coma device (a device devised by A. Sehr for testing the centering of telescopes) is in an advanced state of manufacture. Depending on priorities, pressure on development capacity and availability of suitable products from industry, it may be in ESO's interest to buy a complete instrument. In the case of an instrument in which optics assumes a dominant role, the definition and processing of the contract followed by acceptance and testing, form apart of our work which should not be underestimated. An example is the BolJer and Chivens spectrograph which has just been delivered for immediate use at the Cassegrain focus of the 3.6 m telescope as soon as this focus becomes available.

5. Other ESO Equipment Coming now to the general support side of the Observatory's other equipment apart from the 3.6 m telescope, the development of a novel off-set guiding system tor the 1 m Schmidt telescope should be mentioned. This will permit off-set guiding even with the objective prism. The optical design is complete and its manufacture should be possible soon. Preliminary work has also been completed for ordering a new "blue" Schmidt plate which should make the Schmidt telescope more effective in the blue spectral region. Other projects actively being pursued are improvements in the Zeiss camera (TV guiding on the 1.5 m telescope) and the Echelec spectrograph.

6. Other Observatories and Institutes Finally, the OG has fruitful contacts with observatories and institutes of the member states. These include assistance and advice (usually in both directions) with the Pic-du-Midi and OHP in France, with Danish observatories (e.g. supply of a focal reducer), cooperation on optics with ESA in the working group of aSpace Astrometry project, and supply of optics for holographic grating production for Göttingen Observatory. Last but not least, our "sister"organization in Geneva, CERN, has built a prototype of the Cerenkov Counter optical system proposed by the OG. We have also assisted them in the manufacturing contracts for eight such systems which are in course of delivery. The result seems very promising and should be of major importance in the CERN research programmes. In this article we have made no attempt to cover in any depth any of our activities, but rather to give an idea how numerous they are. We hope you will be indulgent ifwe have had no time yet for your problem. We hope we can tackle it soon!

Fig. 4. ESO Optics Laboratory. At the right the ACOFAM test bench; lell foreground the stone bench with interferometer; centre background HP 2100 computer.

8

A New Method to Derive the Distances of Spiral Galaxies G. A. Tammann A new method to determine the distances of spiral galaxies has recently been proposed by R. B. Tully and J. R. Fisher (to be published in Astronomy and Astrophysics, 1976). Their method is remarkable for two reasons: (1) it uses a distanceindependent parameter which is measured at radio wavelengths (21 cm); so far radio astronomy has been slow in

Professor Gustav Tammann of the University of Basel, Switzerland, is presently spending part of his time with the ESO Scientific Group in Geneva as associate astronomer. He is weil known for his work on the extragalactic distance scale, culminating in arecent, but already classical series of papers in the Astrophysical Journal, under joint authorship with Dr. Allan Sandage of the HaIe Observatories. We are delighted to bring here the very latest news about the recently discovered 21-cm-line galaxy luminosity (and thus distance) indicator.

providing good distance determinations; and (2) the parameter correlates with the total optical luminosity of a spiral galaxy; up to now only few, if any, luminosity indicators, besides van den Bergh's luminosity classification, have been known for spiral galaxies. The new method uses the line width of the 21-cm line of external galaxies as measured with single-dish radio telescopes. The width of the Doppler-broadened line is determined by the internal motion of the neutral hydrogen, i.e. essentially by the rotation of the galaxy. Hence, the total line width is expected to be equal to 2· Vmax ,where Vmax is the maximum rotational velocity. Of course the line width can only be determined for galaxies with well-determined 21-cm-line profiles, and this limits the method to spiral and late-type irregular galaxies. It is also evident that the line width reflects only the component of vmax in the line of sight; the true line width, denoted LI Vdl' is directly observable only in edge-on galaxies-the measured line width of other galaxies must be corrected for the inclination i between the rotation axis and the line of sight (by dividing by

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The correlation be\ween the absolute photographic magnitude Mg·~ (corrected for absorption in our Galaxy and within the exlernal galaxy) and log LI vi, (the inclination-corrected 21-cm line width) for galaxies with independently-known distances (from Sandage and Tamman, 1976). Spirals of different types are sl10wn with different symbols.The error bars indicate the observalional uncerlainlies of

LI v2i,.

9

sin i). Since the correction becomes very large for nearly face-on galaxies, their true Iine width can not be rel iably determined. So me correlation between the true line width Llv2i1 and the optical absolute magnitude M of a galaxy is expected: the line width is correlated with the rotation velocity of a disc galaxy and hence with its mass, and the mass of a galaxy determines to a large extent its luminosity. The only surprising result is that Tully and Fisher found such a tight correlation between line width and absolute magnitude in spite of the fact that other independent parameters were neglected-parameters which are expected to influence as weil the mass and luminosity (Iike the radial distance of the point where Vmax occurs, the form of the rotation curve, and the subtype of the spiral galaxy). Thus the theoretical background of the correlation is not yet understood, but the good empirical correlation between LI V2', and M suggests that it should be used as a tool to determine distances. Tully's and Fisher's main result was a confirmation (to within ± 10 per cent) of the distances to the M 81 and M 101 groups of galaxies, which formed the basis forthe new value of the Hubble constant of Ho = 55 km S-1 Mpc- I . However, from a few spiral galaxies, which are members of the Virgo cluster, they determined a distance of this cluster of only 13 megaparsec (cf. Bull. Amer. Astron. Soc. 7, 426, 1975), which is in open contradiction with the distance of 20.0 ± 2.0 Mpc indicated by several other good distance indicators. This contradiclion seemed to cast considerable doubt on the 21-cm-line method. In a rediscussion of the Virgo cluster problem, A. Sandage and G. A. Tammann (to be published in Astrophysical Jour-

The new empirical correlation between the 21-cm line width and the opticalluminosity of favourably inclined spiral galaxies al ready seems to provide a valuable check of the extragalactic distance scale, which is characterized by a Hubble constant of 55 km S-I Mpc- 1 . Once the theoretical background of the correlation shall be better understood, and accurate determinations of the inclination angle and of the internal absorption shall become possible, 21-cm line widths may become a major route to the distances of many late-type field galaxies. This would be yet another example for the prolific interaction between radio and optical observations.

STAFF MOVEMENTS

The ESO Administration now in Munich

Since the last issue of the "Messenger", the following staff movements have taken place:

On July 1,1976 the ESO Office of the Director-General was transferred from Hamburg-Bergedorf to Garehing near Munieh, about two kilometres from the site reserved for the conslruction of the European Headquarters of the Organization. (See "The Messenger" No. 4, March 1976).

ARRIVALS Munich Marianne Fischer, German, secretary Hannelore Heubes, German, clerk-typist Lindsay Holloway, British, clerk-shorthand typist Martin Hoffmann-Remy, German, accountant Imke Heidtmann, Swedish, clerk-typist Geneva Walter Nees, German, technical assistant Jacques Ottaviani, French, laboratory technician Chile Max Jean Lizot, French, optical engineer

DEPARTURES Hamburg Petrus Huijmans, Outeh, finance officer Gladys Wastavino, German, clerk-typist Ulrike Schütz, German, secretary Ingrid Knoth, German, administrative assistant Brenda BÜlow, British, secretary Heinz-Werner Marck, German, accountant Chile Emile Leroy, Belgian, senior engineer Martin de Groot, Outeh, astronomer Horst Franz, German, engineer Lennart Ulltjärn, Swedish, programmer Andre Theisen, Belgian, personnel officer

10

nal, Novem ber 15, 1976) have used a larger sam pie of cl uster galaxies and have found from the LI V211 data a cluster distance of 19.2 _ 2.0 Mpc. This is now in very good agreement with other distance determinations and with a value of Ho = 55 km s-' Mpc- 1. How can it be explained that the 21-cm distance of the Virgo cluster seemed originally so smalI? The reason is an additional difficulty: the apparent magnitude of external galaxies is dimmed by the internal absorption of interstellar dust. The amount of internal absorption increases with the inclination angle i. For nearly edge-on galaxies the magnitude correction is very large (more than one magnitude), but actually the exact amount is still poorly known. Thus the above-mentioned advantage of edge-on galaxies for the determination of the true 21-cm line width is offset by their large and uncertain correction for internal absorption. It seems therefore that galaxies with intermediate inclination (30° i 70°) should be given the highest weight.

:s :s

When the ESO Council at its December meeting last year accepted the German Government's offer of a site and building for the futu re headquarters of the Organization at Garehing near Munieh, hardly anyone of the Hamburg staff thought that he would be in Munich only half a year later. But the decision to transfer the Office of the Director-General to Garehing was taken without delay. Already in February lhe staff was officially informed that the Administration would move to Garehing towards the middle of the year. The decision for this move-before the construction of the headquarters had even started-was mainly taken in order to be on the spot during the construction activities and to improve communications with Geneva. Also, when in 1979 the ESO departments in Geneva in their turn move to Garehing, theAdministration will be in a beller position to assist them and to facilitate a smooth continuation of activities. Most staff members saw no difficulty in following the Administration and began immediately to search for suitable accommodation. The many possibilities for sports and excursions in the surroundings of Munich will partly compensate them for the separation from their relatives and friends in Hamburg. A few staff members were unfortunately not able to follow the Organization and decided to stay in Hamburg. The removal of the Office of the Director-General took place between June 24 and 30, and most staff members managed to have their private removal done during the same period. On July 1, the Office of the Director-General resumed its activities and everybody has been working hard ever since to make up for the time lost during the removal period. The staff members who decided to stay in Hamburg have meanwhile been replaced and business operations have now returned to normal.

Minor Planets Discovered at ESO Since the discovery on January 1,1801 of the first minor planet (asteroid), more than 2,000 have been observed and catalogued. They have once been called "the vermin of the sky" by a distinguished astronomer and not quite without reason. Most of them move in orbits of low inclination, i.e. close to the Ecliptic (the plane of the Earth's orbit around the Sun), and photographs of sky areas in the neighbourhood of the Ecliptic always show some of these minor planets. It goes without saying that the larger the telescope, the fainter are the planets that can be recorded and the larger are the number that may be seen on a plate.

1. Trails on ESO Schmidt Plates The ESO 1 m Schmidt telescope combines a large aperture with a fast focal ratio (f/3) and is therefore an ideal instrument for the discovery and observation of minor planets. On long-exposure plates, each minor planet in the fjeld is recorded as a trail, due to the planet's movement, relative to the stars, during the exposure. On the ESO Quick Blue Survey plates (cf. Messenger No. 5, June 1976), which are exposed during 60 minutes, most asteroid trails are about 0.3 to 0.7 millimeters long. Asteroids down to about 19~Q--19m5 are seen on these plates. (Fainter minor planets may be observed if the telescope follows the planet, whereby the light is concentrated on the same spot of the photographie plate and not "wastefully" spread along the traiI.) Several of the ESO QBS plates show something like one hundred asteroid trails! It is completely impossible from a

Minor planet 1975 YA was lound in December 1975 at Haie Observatories by C. Kowa!. It moves in an orbit slightty outside that 01 the Earth. During its closest approach to the Earth in 1976, which took place in late June, it came within 55 million kilometres. Unlortunately, at that time it was lar south and could not be observed with northern telescopes. However, this trail 01 1975 YA was obtained on July 3, with the ESO Schmidt telescope under rat her bad weather conditions. Exposure time 10 min on 103a-0 emulsion, magnitude 01 1975 YA approximately 17.4. The position has al ready enabled an improved orbit to be computed at the Minor Planet Center at the Cincinnati Observatory.

practical point of view to measure and follow up so many asteroids and the ESO astronomers who work with the Schmidt plates have therefore taken the natural decision that only "interesting" planets will be re-observed in order to establish their orbit.

2. "Interesting" Minor Planets

This 5-millimetre asteroid trail was lound on a 60 min ESO Schmidt plate, taken on October 2, 1975. The asteroid moved with tt,e unusually high speed 01 2.5 degrees/day, indicating that it was rather close to the Earth. By astrange coincidence, the trail is situated almost at the very centre 01 the Sculptor dwarl galaxy, a member 01 the Local Group 01 Galaxies,

But when is a minor planet "interesting"? Clearly, first of all when it is large (brig ht) or if it follows a path that deviates significantly from that of most other planets. Therefore, the positions of bright trails are regularly checked with the "Minor Planet Ephemeris" Yearbook to see whether the trail belongs to an already known planet. "Long trails" (Ionger than 2 minutes of are, i.e. a motion larger than 48' /day, which indicates that the asteroid is rather close to Earth), are also picked out. So are trails which are found far from the Ecliptic, pointing to an unusually high orbital inclination. In this way, several tens of "interesting" minor planets have been detected on ESO Schmidt plates, Due to the extremely heavy workload on the ESO Schmidt telescope, only a few of these discoveries have so far been followed up, Plates of solar-system objects (minor planets and comets) have in practice only been obtained during bad weather conditions or with moon when no other plates were scheduled or could be taken. Examples are two new planets of the Phocaea group, one ofthe very rare Pallas family (only 5 known), and one Apollo-type asteroid (1975 TB). In all ca11

ses the plates were measured at ESO-Geneva and the orbits were computed by Dr. B. Marsden, Smithsonian Observatory, Cambridge, Massachusetts, USA.

H.-E. Schuster and R. M. West will start using the ESO 40 cm astrograph from October 1976. By using sensitized photographic plates they hope to be able to observe all but the faintest of these asteroids, which must still-if possible-be observed with the Schmidt telescope.

3. Asteroids Recovered It frequently happens that a minor planet is so far south that it cannot be observed with telescopes in the northern hemisphere. If, moreover, the planet is on the "critical" list, i.e. its orbit is not accurately known and it may therefore get lost, observations by southern telescopes become urgent. The ESO 1 m Schmidt telescope is one of the most efficient southern telescopes for such work and during the past year, several "critical" observations have been made. For instance, a valuable observation was made on June 12, 1976, at declination -58~5, of Apollo-type asteroid (1580) Betulia, when it was rapidly receding from Earth after the close encounter (19.5 million km) on May 23,1976. On the night of the ESO observation it was al ready at distance 53.4 million km and of magnitude 15. In order to improve the possibilities for following up the discoveries of new asteroids (and making urgent observations of already known ones), ESO astronomers A. B. Muller,

4. Why Observe Minor Planets? Some people may weil ask why astronomers still observe minor planets. With over 2,000 known, what do a few more or less matter? They will probably agree that a thorough knowledge of asteroid orbits may be useful when their greatgrandchildren make the trip to the Jupiter-Ganymede base. But even now the minor planets are important enough to justify continued observations. Their orbits outline the gravitational field of the solar system and their distribution speaks of events in its early history. The physical study of asteroids shows us early solar-system matter, and a soft landing on a suitable asteroid is quite possible within the next decade. As a matter of fact, one of the top-candidates for this honour, Minor Planet 1976 AA, was discovered with the Schmidt telescope on Mount Palomar, California, in January 1976. So the Europeans, keep trying l

Instrumentation Plan for 3.6 m Telescope A new and updated plan for the instrumentation of the 3.6 m telescope has been developed within ESO. The plan, wh ich covers instrumentation developments for the period 1977-1980, was presented on May 12 by the Director-General to the Instrumentation Committee, which gave its unanimous support. The plan will be considered by Finance Committee and Council later this year.

A first step in the preparation of the instrumentation plan was a survey of the scientific programmes wh ich the users of the ESO facilities wish to carry out and of the instrumental parameters they consider optimal. For this survey, questionnaires were sent to all person? who have used the La Silla facilities during the last five years. The response was very good with nearly half of the astronomers providing replies. Research plans cover a very wide range of subjects. Roughly one-third of the respondents wish to engage principally in extragalactic and nebular work. Most of the others are planning studies in stellar spectroscopy, especially at medium and high resolutions. Among the instrumental wishes, a rather high-dispersion Cassegrain spectrograph is at the top of the list. The use of efficient modern panoramic detectors is regarded as essential by many respondents.

spectrograph with attached image-dissector scanner and a vidicon for direct imaging. In the instrumentation plan, several new developments are foreseen. Highest priority is given to a cross-dispersed Cassegrain echelle spectrograph and to a high-resolution coude spectrometer. The former should allow the observation of faint stars at reasonably high dispersions (5 A/mm) when used in conjunction with a modern detector, and the latter observations of brighter objects at very high spectral resolution. Other spectrographs, including one for the near infrared, and a radial-velocity photometer are also being planned. The acquisition of a variety of the newer detectors forms an important element in the plan, since these detectors and the equipment needed for their effective use are essential both for direct imaging and for spectroscopy. Infrared developments also are given much attention. A special top ring with wobbling secondary is foreseen for the telescope to make it reasonably "clean" in the infrared,

Some instrumentations forthe 3.6 m telescope is already under construction at present. Included are various cor-

and photometric and other accessory instruments are

rectors, a 4-6-channel photometer, a low-dispersion

planned.

12

Clusters of Galaxies Why do galaxies cluster? Are these clusters stable over long periods or will they slowly disperse? Is there "hidden" mass in the galaxy clusters? These problems are central in current astronomical research, and the answers may tell us how the very young universe looked like, some 15,000-20,000 million years ago, Dr. Jürgen Materne from the Hamburg Observatory holds a fellowship with ESO's Scientific Group in Geneva. Here he teils what is being done at ESO in this important field of astronomical research: know that many of the nebulae were far outside our own galaxy, the Milky Way, Nevertheless, already the Herschels no-

The basis of one of the large catalogues of galaxies-the NGC catalogue-was laid by observations by the Herschel family of astronomers, nearly two hundred years ago. In this catalogue, galactic nebulae and extragalactic objects were

ticed that the nebulae (in our case the galaxies) often formed groups. They detected among others the Virgo and Fornax

still mixed, because the astronomers at that time did not

clusters.

~

.

. .' "

.

.

_.

.'

"

"

,"

.

"

.,

...

~

,~

.

.'

..

.. ."

This is the centre 01 the medium-size Fornax cluster of galaxies, wh ich also contains a strong radio source, The cluster was photographed with the ESO Schmidt lelescope. The beauliful bright spiral galaxy with the pronounced bar is NGC 1365. At least lwenty-live other galaxles may be seen in this photo.

13

',.

Groups and Clusters

centre of the cluster. A programme is now underway at ESO to measure the internal velocity dispersion of such super-

The difference between groups and clusters seems to be artificial, it is a question of richness: a group mostly contains from a couple to a few dozen galaxies, a cluster may have

giant galaxies in order to deduce their masses and to confirm if they are really, as so me astronomers surmise, one hundred times more massive than normal elliptical galaxies.

from around fifty members like the Fornax cluster to ten thousand like the Coma cluster. In addition to these, we have

Irregular and loose clusters, on the other hand, have a large fraction of spiral galaxies and it seems that the hydrogen

so-ca lied "solar system"-like groups, a large galaxy with a

content in the spiral galaxies depends on the type of the sur-

few dwarf companions. Our Milky Way is a fairly large galaxy and has several such small companions: e.g. the Sculptor, the Draco and the Ursa Major galaxies. The c1ustering over

rounding cluster.

all sizes is amazing and is not at all explained by the current

Missing Mass?

theories of galaxy formation. With all these different sizes, a few questions arise at

The correct membership assignment is also vital for calcula-

once: (1) 00 the clusters show substructure, or (2) do clusters of galaxies form superclusters, and (3) do real field galaxies exist, i.e. galaxies which do not belong to any cluster of galaxies?

ting the mass of clusters of galaxies and for investigating the dynamical state of a cluster. Often one finds that the sum of the masses of its member galaxies, i.e. the "visible" cluster mass, is not enough to make the cluster gravitationally stable, to keep it from falling apart. Is there a hidden, "invisible" mass, perhaps as an intra-cluster medium? But neutral hydrogen has not yet been found in large amounts, so Materne

Superclusters? The French-American astronomer de Vaucouleurs claims that the nearby groups of galaxies, including the Local Group to which our Milky Way belongs, are contained in the Local Supercluster with the Virgo cluster at the centre. But this ist questioned by other astronomers who say that the Local Supercluster is only a chance configuration in the sky. Chincarini and Rood recently found a companion cluster of galaxies to the Coma cluster. These two (and others?) may form a supercluster. On the other hand, the application of the mathematical tools of cluster analysis which we are developing at ESO, shows that the Fornax cluster for example tends to break down into relatively well-defined subclusters, although it is not completely clear at the moment how significant these subclusters are. And the problem whether the spiral galaxies and the elliptical galaxies in the Virgo cluster form different subsets is not solved either.

Field Galaxies Only very few field galaxies have been detected but it is always difficult to be sure if they do not belong to a nearby cluster with high internal velocity dispersion. And it is nearly impossible to find out whether seemingly single galaxies do not form small clusters with dwarf galaxies (to build what is called Hyper-galaxies by Estonian astronomer J. Einasto), because these dwarf galaxies are too faint to be observed. Although the problems of how to define a cluster of galaxies correctly and how to assign the proper membership of individual galaxies are not solved, astronomers try to look for differences in the contents of different clusters. Rich and dense clusters contain mostly elliptical galaxies and sometimes a supergiant elliptical galaxy with a large halo in the

14

and Crane started collaborations with radio astronomers to look more carefully for hydrogen in small clusters. In rich clusters, however, X-ray radiation has been detected. That means that some clusters are filled with a very hot gas, but unfortunately the amount does not seem to be enough to keep the cluster together.

The ESO Programme In order to tackle some of these problems we start this winter at ESO a programme to measure the radial velocities of galaxies in the region of the Eridanus, Fornax and Doradus clusters as weil as possible.These velocities must be measured with high precision, because the subgroups have only a velocity dispersion of around 40 km/sec. Then we can test and refine our new models of clusters. We shall also try to detect the hot gas in the optical region by measuring the Hr~ emission with a modified photometer. In a long-range programme in collaboration with other institutes, we shall determine the velocity distribution and the distribution of galaxy types and luminosities in X-ray clusters and non-X-ray clusters. We think that all these observations will give us a better insight into the phenomenon of galaxy clustering.

Tentative Meeting Schedule The lollowing dates and loeations have been reserved lor meetings 01 the ESO Couneli and Commlttees: Oetober 26 Oetober 28 November 25/26 Nov. 30/Dee. 1 Deeember 2/3

Instrumentation Committee, Garehing Committee 01 Couneil, Garehing Observing Programmes Commlttee. Amsterdam Flnanee Commlttee. GarehIng Couneil, Munieh

On the Vertical Support of Astronomical Research in Cassegrain Cages Yes, you are right: these three chairs represent the latest in European modernityf ESO is proud to present, probably for the first time in the history of astronomy, the autumn 1976 fashion in astronomical furniture. But to avoid misunderstandings with the auditors, let us quickly affirm the great importance of these pieces of equipment for the safe performance of observational astronomy on La Silla. Briefly explained, since most human beings, astronomers included, unfortunately do not equal Tarzan in physical strength and agility, they must be firmly supported when taking a ride in the spacious Cassegrain ca ge of the ESO 3.6 m telescope (at the 10 wer end of the telescope tube). To solve this mainly anatomical problem, the braintrust of the ESO Mechanical Group in Geneva, headed by Mr. W. Richter, studied the suspension of astronomical bodies at various elevations and angles. We are happy to prove the survival of the courageous v~/unteers by publishing this report, which was compiled by Mr. Richter, after the successful termination of the experiments: To work as an astronomer at the Cassegrain focus of a big telescope oHen causes problems because the instruments there are not so easily accessible. Even if one assumes that the astronomer needs not to spend long time in the cage, because the observational data nowadays are transmitted directly to a computer terminal, there ist always the necessity to go into the cage for the initial adjustment of the instrumentation which is becoming more and more complex.

Many trials have been made to design astromer's chairs for the Cassegrain areas of large telescopes. However, most of these solutions must be abandoned because the chairs become too space-consuming in the cages. Now ESO proposes for its 3.6 m telescope a new approach which is the result of a development which is shown by the three photos:

3

-

The first version (No. 1) was designed for observations within a range of ± 15° around the zenith. We found that it was too difficult to handle this chair due to its weight of 24 kg.

-

The second version (No. 2) was lig ht enough (10 kg) and covered a much wider range, but it was much less comfortable to sit in such a big ring than we thought. The third version (No. 3) looks more promising: the chair can be used wherever the telescope points between zenith and horizon. Easy to operate are the adjustment

possibilities which allow to turn the chair around its stem, to move it up and down and to turn the chair in the ring. It is also not difficult to move the whole unit-only 10 kg -from one hole in the cage-floor 10 the next. The main technical problem was to get the overall size and the weight down. Now it is up to the astronomers to find out how this chair suits their needs. They will probably say that handling and sitting on this chair are sufficiently comfortable. However, one needs some experience to select the correct hole in the floor and sometimes it is difficult to climb up to the chair. 15

ALGUNOS RESUMENES

Terminado el montaje dei telescopio de 3,6 m En los primeros dias de agosto, nada mas aeabar de eseribir estas lineas, la eonstrueei6n meeaniea dei teleseopio estaba easi terminada. Tres meses de arduos trabajos fueron neeesarios para Ilegar a esta fase. Hubieron de abrirse mas de 150 eajones y de transportarse los eomponentes dei teleseopio, pieza por pieza, a traves dei kil6metro y medio que distaba entre el lugar de desembalaje y el edifieio dei teleseopio. Los trabajos de limpieza y montaje se real izaron en la planta baja, antes de que la grua de 35 toneladas, situada sobre la eupula, elevara las piezas a la plan ta de observaei6n. Aigunas piezas o bloques armados pesaban mas de 30 toneladas. La pieza mas pesada fue la herradura dei eje polar ya ensemblada, eon un peso de 40 toneladas! Co mo en Europa ya se realizo un montaje previo a tftulo de prueba, los problemas que se presentaron d urante los trabajos de montaje en La Silla fueron de menor importaneia.

Astr6nomos suizos en La Silla Siguiendo un aeuerdo estableeido en 1974, el Consejo de la ESO autorizo al Observatorio de Ginebra la eonstrueeion de una estaeion provisional de observaeion en La Silla. Dieha estaei6n, que fue instalada el ario pasado, tiene una eupula de 4,60 m de diametro y esta unida a una ea-

First Slides tram ESO Schmidt Telescope Available Aseries of 20 slides from the ESO 1 m Schmidt telescope is available at the European Southern Observatory. The 5 x 5 cm black-andwhite slides are accompanied by brief descriptions and show some of the southern sky's most spectacular and beautiful objects, including the Magellanic Clouds, the Eta Carinae nebula and Omega Centauri. The price of this magnificent slide set is Swiss francs 16,- (or the equivalent) for Europe, and US$ 6,- by surfacemail to all other countries, or US$ 8.50 by airmail (to be paid in advance). Send cheque or bank draft to: EUROPEAN SOUTHERN OBSERVATORY Schleißheimer Straße 17 0-8046 Garchlng b, München COMMERZBANK. München Account No. 210 2002

seta de servieio. Esta easeta alberga un puesto de observaei6n, un ban co de trabajo eon equipos para reparaeiones de emergeneia y una pequeria eoeina. Bajo la eupula se ha instalado una mesa eeuatorial, sobre la que hay montado un teleseopio Cassegrain de 40 em de anehura y 7,20 m de longitud foea!. EI teleseopio esta equipado eon un foto metro fotoeleetrieo eonveneiona!. Desde noviembre de 1975, feeha en que se puso en servieio la instalaei6n, han aeudido a La Silla repetidas veees grupos de dos astr6nomos dei Observatorio de Ginebra. Diehos astronomos han quedado sumamente impresionados de la ealidad fotometriea dei sitio y opinan que el numero de noehes elaras es tan elevado que el trabajo de observaei6n resu Ita fatigante hasta para sus mejores espeeialistas. ."

,

LA·TEST' NEW·S

' . '.:

Professor A. Blaauw Next President of the lAU We have just learned that the Exeeutive Committee of the International Astronomieal Union has nominated the former Direetor-General of ESO (1970-74), Professor A. Blaauw, for eleetion to the presideney of the lAU (1976-79). The eleetion will take plaee du ring the seeond plenary meeting on September 2, 1976, at the time of the XVlth General Assembly in Grenoble, Franee. By that time, this issue of the Messenger will already have been published, but trusting that the lAU will not deviate from the traditional praetiee of eleeting a presidential nominee by aeelamation, we extend our heartiest eongratulations and best wishes to Professor and Mrs. Blaauw. Professor Blaauw is the seeond ESO Direetor-General to reaeh this high office; his predeeessor in ESO, Professor O. Heckmann, was lAU President from 1967 to 1970. Of the six Presidents of the ESO Couneil, three have also been Presidents of the lAU: ProfessorsJ. H. Oort (ESO Couneil: unti11965, lAU: 1958-61); B. Lindblad (ESO Couneil: 1965, lAU: 1948-52); and B. Strömgren (ESO Couneil: 1975-, lAU: 1970-73).

16